They haven't lost meaning, you can still wait a bit to get your game cheaper. It does usually follow a pattern of: opening sale 10%, full price for a bit, seasonal sales 10-50%, eventually up to 90% off during seasonal sales.
Sure. But have you not noticed how the same, now oldish, games go on sale for the exact same amount for years and years?
I can tell without looking that Cities: Skylines is sold for 6.99 euro. Or the latest Civilization game at 15 euro. Or bioshock infinite at 7.99 euro or so.
What's the problem with that? Terraria has been on sales for 2$ for ages now, that doesn't mean it isn't a bargain to buy at that price instead of 10 or 12 that it is regularly.
No problem at all. It's just not special anymore. Do you not remember the first few steam sales? Everyone's mind was blown because there was nothing like it until that point